Electrical contacts

ABSTRACT

An electromagnet relay carries a resilient conductive wire pad which is compressed when the pair of contacts mate to minimize contact bounce and attendant mechanical shock, and which provides contact wiping to provide reliable electrical contact.

United States Patent n 13,613,036

[72] Inventor John 0. Kurtz [5 61 References Cited l.0. Box 79, Smithville Flats, N .Y. UNITED STATES PATENTS 3 f fg 3,227,840 1/1966 Reed et al 335/196 2 d ml 2,528,086 10/1950 Schenck..... 200/166 11 l 1 a 6 706,759 8/1902 Kennedy 335/196 Primary Examiner-Harold Broome 54] ELECTRICAL CONTACTS Att0rneyRichard G. Stephens 2 Claims, 9 Drawing Figs.

[52] U.S. Cl 335/196, BSTRACT: An electromagnet relay carries a resilient con- 200/166 ductive wire pad which is compressed when the pair of con- [51] Int. Cl H0lh 1/24 tacts mate to minimize contact bounce and attendant [50] Field of Search 335/ 196, mechanical shock, and which provides contact wiping to pro- 193; 200/166 H, 166 C vide reliable electrical contact.

PATENTEDUET 12 ml SHEET 1 a? 2 FIG.

FIG. Io.

FG.2c

FIG. 2b

INVliN/(IR. JOHN O. KURTZ PATENTEDUBT 12 ml 3,613,036

' SHEET 2 OF 2 FIG. 3a FIG. 3b

FIG. 3c FIG. 3d

ELECTRICAL CONTACTS This invention relates to electrical contacts, and especially to contacts used on electromagnetic switches, such as relays and contactors, though basic principles of the invention are applicable to various other electrical contacts. Many known forms of electromagnetic relays or contactors comprise a magnetic armature which is movable from one position to another by the attractive force of an electromagnet, usually against the force of a spring which returns the armature to its original position when the electromagnet is deenergized. Themovable armature carries an'electrical contact which mates with a stationary contact at one position or another of the armature, or which mates with two separate stationary contacts at the two positions of the armature. Many relay armatures move plural movable contacts to and from respective stationary contacts, or in between respective pairs of stationary contacts.

The desired speed of relay operation, and/or the amount of contact pressure desired between a pair of mated or closed relay contacts often requires that a powerful electromagnet, and sometimes a powerful return. spring, be employed. In some relays the armature is arranged to s 'ke a stop at each end of its travel. If either the armature or the stop has any resilience whatever, as is inevitably the case, the armature tends to bounce when it strikes the stop, since the mass of the armature, the resilience of the armature and/or stop, and the inelasticity of the armature and/or stop form a second order mass-spring-damper system. The oscillation of the armature relative to the stop is usually rapidly damped out as the energy stored in the resilience of the armature and/or stop is converted to heat. To insure contact closure in the face of contact wear, and to provide a finite contact pressure during closure, the armature is ordinarily allowed to travel further in both directions than the nominal amount of travel needed to close the contacts, and the overtravel of the armature allowed to flex a spring arm or blade upon which the movable contact is carried. Sometimes the movable contacts are carried on essentially rigid amis relative to stationary contacts carried on flexible anus, and sometimes both the movable and the stationary contacts are carried on flexible arms. The amount by which the movable and/or stationary contact arms must be allowed to flex in order to provide a desired contact pressure, or in order to insure reliable contact in the face of contact wear, and the amount by which they must be allowed to flex so that all contacts of a plural or multipole relay reliably engage, tend to require considerably more contact arm resilience than'the amount to which that in the armature and stop may be reduced. The interposition of one or two spring arms or blades between the movable armature and the stationary structure upon which the electromagnet is mounted, provides a modified mass spring damper system, so that the relay contacts tend to bounce considerably more. Decreasing the resilience of the contact arms to decrease bounce allows less tolerance for contact wear, and requires that plural poles of a relay be more precisely aligned. Relay contact bounce frequently causes serious electrical noise in electronic systems which incorporate relays. It is one important object of the invention to provide an improved electromagnet relay having a contact system less susceptible to contact bounce. Another object of the invention is to provide a relay which is less susceptible to contact chatter caused by coil hum when alternating-current energization is used.

When a conventional relay is operated, the sudden mating of a pair of contacts often creates a mechanicalshock which propagates from the contacts to base structure, such as a circuit board or a chassis, and to surrounding electronic equipment, sometimes introducing noise or otherwise interfering with the operation of the electronic equipment. The closing of a pair of contacts also creates an audible noise, which, in certain applications, is annoying to humans. It is another object of the present invention to provide improved relays wherein such mechanical shocks and audible noises are minimized:

Reliable electrical contact between a pair "of mating relay contacts requires that the mating portions of the 'pair of contacts either be free of oxidation and various other surface I films, or that the mating portions be wiped to remove such films as the contacts are closed, and a variety of contact wiping techniques are disclosed in the prior art. Another object of the present invention is to provide an improved relay contact arrangement which automatically provides effective contact wiping.

Other objects of the invention will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts, which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature invention reference should be had to the description taken in connection with drawings, in which:

FIG. 1 is a side view, with certain portions cutaway, of one embodiment of the present invention.

FIG. la is .a view of a portion of the relay of FIG. 1 showing the relationship between a pair of mating contacts.

FIG. 2a is a plan view of a plurality of helical coils which may be used to provide one form of compressible conductive pad usable inthe invention.

FIG. 2b is a view of a piece of woven wire sheet which may be used with the coils of FIG. 2a in order to construct one form of compressible conductive pad.

FIG. 2c is a side cross section view of a compressible conductive pad formed'by assembling the coils of FIG. 2a and the woven wire sheet of FIG. 2b.

FIGS. 30 to 3d illustrate modified contact arrangements which may be used in the relay of FIG. 1.

The improved relay shown in FIG. 1 comprises a base (not shown) having an electromagnet l2 fixedly mounted thereon. The ends of the electromagnet coil are connected to stationary terminal posts 13 and 14. A soft-iron armature bar 16 is pivotally mounted at 16g on a shaft (not shown) extending normal to the plane of FIG. I. A movable contact arm 18 is riveted to armature 16 at 19,19, and flexible wire 20 connects contact arm18 to terminal post 22. A tension spring 24 is connected between a tab on armature l6 and adjustment screw 25 threaded in fixed post 26 and locked in place by lock nut 27. Armature l6 and movable contact arm 18 are shown in midposition between a pair of fixed contact bars 28 and 30. Carried on opposite sides of movable contact arm 16 are a pair of resiliently compressible conductive wire pads 32 and 34 which are an essential feature of the invention, and which will be described below in detail. When electromagnet 12 is not energized, tension spring 24 pivots armature l8 clockwise from the position shown in FIG. 1 so that compressible wire pad 34 engages stationary contact bar 30 and is compressed as shown in FIG. la. When electromagnet 12 is energized to rotate arma ture l6 counterclockwise, compressible wire pad 32 is similarly compressed against stationary contact 28, and pad 34 returns to its original uncompressed shape. In FIG. 1 pads 32 and 34 are shown having the same thickness, which is preferred when the maximum force of electromagnet 12 is approximately thesame as the force of spring 24 when pad 34 is compressed as shown in FIG. la. Where the two mentioned forces differ, the two pad thicknesses may differ.

. Pads 32 and 34 each comprise a compressible pad formed from one or several fine wires having good conductivity, such as beryllium copper. Wire having good springiness but poorer conductivity, such as steel wire, may be plated to improve its conductivity and then used in certain applications. Solid (i.e. unplated) wire is preferred, however, so that wear does not reduce its conductivity. Wire having a square, triangular or other noncircular cross section, so as to provide sharp edges, is preferred. In various applications of the invention the pads may take various shapes, such as rectangular or circular. One or several strands of wire may be laid in a cavity having the desired shape, with a given strand being bent and trained back and forth and up and down and around itself in the cavity,

will in part be obvious and and objects of the following detailed the accompanying thereby to provide an oversize, springy tangle" of wire. A die then may be forced into the cavity to compress the wire mass sufficiently to provide a set conforming to the desired shape, without completely crushing the mass so that it has no resilience. Use of a single piece or only a few strands for a given pad is ordinarily preferred, in order to minimize the number of loose ends, and the ends are poked or bent inside the tangle prior to compression, so that no loose ends will protrude from the finished pad, or at least from the top and side edges of the pad, or if desired, any ends of the wire may be welded together. It is desirable that many sections of the wire be trained back and forth across the top of the tangle, so that the finished pad will present a uniform surface without large gaps or holes.

Rather than essentially random formation as desired above, the wire pads may be made by superimposing on top of each other plural strips of loosely woven wire cloth or sheet having warp strands running in one direction and woof strands running perpendicularly thereto, for example, or by superimposing one or several such strips of woven wire sheet on top of a spring means. A form of compressible pad shown in FIG. 2c comprises a plurality of solenoidal coils of wire of the nature shown in FIG. 2a, with various coils differing in coil diameter and winding pitch, and, if desired, coil length and/or coil wire size. Rather than being arranged concentrically, however, the coils are preferably very substantially intermeshed, so that various turns of each coil lie between various turns of other coils. The center section a of a cruciform shaped piece of woven wire mesh having the shape shown in FIG. 2b is placed atop the intermeshed coils. The woven mesh is bent along the dashed lines shown. Portions b, c, d and e form the sides of the pad, and portions f, g, h and i are tucked underneath to form the bottom. The spring constant of the pad may be tailored by selection of the spring constants of the coils, and by the amounts by which the coils are precompressed when the woven mesh is wrapped around them. The edges of the wire mesh may be welded or soldered together at the bottom of the pad, or they may be soldered on a contact arm, in order to hold the precompressed spring means inside the wire mesh. In many applications the wire coils inside the thus-formed pad need not have great conductivity. In some applications of the invention, some or all of the wire coil springs may be dispensed with, and a loosely woven wire mesh instead formed over a non conductive compressible pad, such as a piece of foam rubber, although compressible pads having many wires which rub against each other as the pad is compressed is preferred where decreasing contact bounce is deemed important. Instead of, or in addition to the coil springs shown in FIGS. 2a and 2c, the pad of FIG. 2c may include one or more tufts or small bundles of fine wire, similar to small bunches of steel wool.

Irrespective of how the compressible pad is formed, it is highly desirable that very many of the sections of wire inside the pad frictionally bear or scrape and twist against many other sections of wire, so that compression and decompression of the pad will cause many edges of the wire to rub against many other edges, thereby dissipating a larger amount of energy of compression as friction or heat, and providing a conductive spring means which has a much lower coefficient of restitution and hence a much greater damping factor than or dinarysprings. If a pad such as 32 or 34 in FIG. 1 is thus provided with a large damping factor, it will tend to strike a contact bar such as 28 or 130 with a dull thud rather than a sharp snap, and it will have far less tendency to bounce than ordinary prior art contacts. It will also be clear now that the movable contact will apply smaller mechanical shocks to the fixed contact bars, and will create less audible noise than most prior art relay contacts. Furthermore, because the resilient pads tend to conform to the surfaces which they strike, precise alignment of a movable contact arm relative to a stationary contact becomes less necessary. Also, some of the vibrations of the movable arm and armature due to hum in those cases where AC energization is used will be absorbed by the compressive pad, due to its low coefficient of restitution, making the relay contacts less likely to chatter.

When the coil (or the return spring) of an ordinary relay accelerates an armature and a movable contact carried on a flexible arm toward a stationary contact, inertia of the movable contact arm and armature cause the flexible contact arm to flex as the contacts meet, and for energy to be stored in the flexible arm. The stored energy then moves the armature in the opposite direction, tending to reopen the contacts, and the movable arm vibrates until the stored energy is damped out. If the fixed contact is also mounted on a flexible arm, some of the energy will be stored in the fixed contact arm and it will also vibrate. The vibrations of a system will have less amplitude and will decay more rapidly if the resilient portion of the system has a high damping factor, or low coefiicient of restitution. In the invention, a considerable percentage of the kinetic energy contained in the inertia of the armature and movable arm is immediately converted to heat as closure of the contacts causes many of the wires of the conductive pad to rub against each other as the pad is compressed. As the pad then tends to expand, further rubbing together of the wires dissipates further energy. Thus the conductive pad acts as a damper as well as a spring, thereby greatly increasing the damping ratio over that of an ordinary relay, and thereby minimizing contact bounce.

As the conductive pad strikes a contact surface, whether it be a rigid surface or the surface of another compressible pad, and irrespective of whether the other surface is flat or not, the compressing of the pad causes some motion of the wires which form the surface of the pad in directions parallel to the surface, thereby causing the wires of the pad to wipe the surface in a number of locations and insure good electrical contact.

When the relay of FIG. 1 is energized pad 32 is compressed against stationary tenninal 28. If electromagnet coil 12 is equipped with various arc-suppression devices, such as resistance (not shown) in parallel with the winding of coil 12 to suppress inductive voltage transients, the attractive force of coil 12 may tend to decrease more slowly than desired when coil 12 is deenergized, and the armature will begin to open contact pair 28-32 only when the torque due to magnet force decreases to where the torque due to spring 24 force exceeds the sum of torque due to magnet force and torque due to friction at pivot 16a. The prior compression of pad 32 will provide some force, however, which will assist in initially rotating the movable arm to open contact pair 28-32.

FIG. 30 illustrates that both of the compressible conductive pads of a double-throw relay may be carried on the stationary contacts rather than on the movable contact, to be engaged by rigid surfaces on the movable contact arm. FIG. 3b illustrates that one stationary contact 28 may carry a compressible pad 28a, while the other carries a rigid surface which engages a pad 34b carried on the movable arm. In FIG. 3b a flat blade spring 24a rather than a coil spring acts as a return spring for the movable contact arm 18. Location of the pads on the stationary contacts allows one to reduce the inertia of the movable arm, of course. FIG. 3c illustrates that a pair of mating contacts both may carry conductive, compressive pads which engage each other as the relay is energized (or deenergized). FIG. 3d illustrates that the contact pads need not present flat surfaces, and that rigid contact surfaces which are engaged by the pads need not be flat. A movable relay armature of a multipole relay may translate a plurality of electrically separate movable contacts, of course, and the application of the invention to multipole relays will be apparent to those skilled in the art in view of'the above disclosure. While the invention has been illustrated in connection with electromagnet switches wherein an electromagnet causes a movable contact arm to pivot, it will readily apparent that the invention is applicable as well to switches where an electromagnet instead translates a movahile contact in a linear manner, applicable to switches where motive means other than simple electromagnets are used, and applicable to switches where the motive means pivots or translates both of a pair of mating contacts rather than moving only one of them relative to a fixed other one.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above demription or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electrical switch, comprising, in combination: first and second stationary rigid electrical contact members mounted spaced from each other, each of said members having a flat surface; a rigid, pivotally mounted, magnetic armature bar, a movable electrical contact member comprising a flat blade, one end of said flat blade being fixedly attached to said armature bar and the other end of said fiat blade extending to the space between said first and second rigid contact members, and first and second conductive resilient pads fixedly mounted on opposite sides of said other end of said fiat blade; an electromagnet mounted on one side of said armature bar and tension spring means mounted on an opposite side of said armature bar so that energization of said electromagnet urges the first of said resilient pads against the flat surface of said first stationary contact and deenergization of said electromagnet allows said tension spring means to urge the second of said resilient pads against the fiat surface of said second stationary contact; each of said conductive resilient pads comprising a multiplicity of helical springs covered by and retained within a piece of woven wire sheet, with said helical springs partially compressed.

2. A switch according to claim 1 in which the multiplicity of partially compressed springs retained within each of said pads includes a plurality of springs of difi'erent diameters, with turns of various of the springs interleaved with turns of others of the springs. 

1. An electrical switch, comprising, in combination: first and second stationary rigid electrical contact members mounted spaced from each other, each of said members having a flat surface; a rigid, pivotally mounted, magnetic armature bar, a movable electrical contact member comprising a flat blade, one end of said flat blade being fixedly attached to said armature bar and the other end of said flat blade extending to the space between said first and second rigid contact members, and first and second conductive resilient pads fixedly mounted on opposite sides of said other end of said flat blade; an electromagnet mounted on one side of said armature bar and tension spring means mounted on an opposite side of said armature bar so that energization of said electromagnet urges the first of said resilient pads against the flat surface of said first stationary contact and deenergization of said electromagnet allows said tension spring means to urge the second of said resilient pads against the flat surface of said second stationary contact; each of said conductive resilient pads comprising a multiplicity of helical springs covered by and retained within a piece of woven wire sheet, with said helical springs partially compressed.
 2. A switch acCording to claim 1 in which the multiplicity of partially compressed springs retained within each of said pads includes a plurality of springs of different diameters, with turns of various of the springs interleaved with turns of others of the springs. 